Blood contains various kinds of lipoproteins. These lipoproteins are classified into chylomicron (hereinafter abbreviated as CM), very low-density lipoprotein (hereinafter abbreviated as VLDL), low-density lipoprotein (hereinafter abbreviated as LDL) and high-density lipoprotein (hereinafter abbreviated as HDL) according to their specific gravity. Each class of lipoprotein has its specific ratio of constituents such as cholesterol, triglycerides, phospholipids and proteins and has a different function in vivo.
In clinical tests, cholesterol in HDL is considered as a negative risk factor for arteriosclerosis and cholesterol in LDL is considered as a positive risk factor for arteriosclerosis. Thus, the determination of cholesterol of such classes is frequently performed in the field of clinical testing.
It has been demonstrated that cholesterol in lipoproteins formed by lipid metabolism and the like is a more closely linked risk factor for arteriosclerosis than LDL cholesterol. An example of the lipoprotein formed by lipid metabolism and the like is RLP.
Recently, a method for the determination of cholesterol in RLP (hereinafter abbreviated as RLP-C) by immunoadsorption method was developed. According to this method, RLP is separated from serum by immunoaffinity chromatography using affinity gel containing anti-apoA-I monoclonal antibody and specific anti-apoB-100 monoclonal antibody which does not recognize apoB-48, and cholesterol contained in the separated RLP is determined. A reagent for the determination of cholesterol in RLP applied in this method is commercially available from JIMRO Co., Ltd. (product: RLP-cholesterol “JIMRO” II) (see non-patent document Nos. 1 and 2). This method for the determination of RLP-C by immunoadsorption method is given health insurance scores by the Ministry of Health, Labour and Welfare in Japan.
However, the above method employs affinity chromatography using antibodies and requires separation of components of a sample, which makes it a cumbersome and time-consuming method.
Also known is a simple and sensitive method for measuring RLP-C without separation of components of a sample (see patent document No. 1).
Patent document No. 1:
                Japanese Published Unexamined Patent Application No. 231597/01Non-patent document No. 1:        
Arteriosclerosis, 25 (9, 10), 371 (1998)
Non-patent document No. 2:
Clinical Chemistry, 48 (2), 217